There are numerous known devices for measuring the dimensions or angular asymmetries of persons or animals.
In particular, WO9908064 describes a device for measuring the width of the mouth of a horse or other animal. The device comprises an elongated crossbar with a graduated scale extending along its length and two contact elements designed to abut against two opposite sides of the animal's mouth. At least one of the two contact elements is movable along the elongated crossbar to obtain the measurement, while the other can be positioned proximal to one longitudinal end. The measurement is obtained by inserting the elongated crossbar inside the animal's mouth and subsequently positioning the two contact elements in line with the left and right sides of the animal's mouth. The measurement of the width can thus be read on the graduated scale.
U.S. Pat. No. 6,178,652 describes a device for measuring a horse's head comprising a plurality of belts designed to be positioned on the horse's head using adjustable closing means. The shape of the belts substantially resembles that of the bridles commonly used for horses. The belts are marked with numbered scales along their length and include suitable reading windows that enable a reading of the lengths associated with the belts. Thus, after adjusting the closing means to make the belts adhere to the horse's head, the measurements of numerous physical lengths of interest can be viewed through the reading windows.
One evident disadvantage of the above-described solutions lies in that neither of the two devices allow for the measurement of any angular misalignments between certain anatomical points of interest, e.g. between the teeth and the temporomandibular joint or the eyes of the animal. The solutions described are restricted to the measurement of lengths, from which it is difficult or impossible to derive an indirect measurement of any angular misalignments with an acceptable degree of uncertainty.
U.S. Pat. No. 5,678,317 describes a device for measuring the angular asymmetries of the human face. The device comprises two shanks hinged to one another so that they can be rotated relative to one another. On one of the two shanks there is a graduated scale that enables the angle coming between the two shanks to be measured. One shank is juxtaposed to the face and aligned with one direction of symmetry on the face, while the other shank is rotated until it comes into line with the physical feature of which we wish to measure the angle of inclination in relation to the selected direction of symmetry. The measurement is obtained by reading the angle on the graduated scale.
One disadvantage of this solution lies in that it is only possible with ease to measure one angle between two directions, but not the dual angular inclination of one plane of interest in relation to a second plane of reference. In the field of animals in particular, as concerns mastication, there are two planes of reference that can be considered, i.e. a plane passing through the anterior sagittal point and the temporomandibular joints, and a plane passing through the anterior sagittal point and the eyes.
The drawback of the above-mentioned instrument is consequently particularly evident in the field of equine species, because it does not enable a measurement of the dual latero-lateral inclination, relating to the incisor plane with respect to the axis of the eyes or to the axis passing through the temporomandibular joints, in combination with the antero-posterior inclination of the horse's incisor occlusal plane in relation to said corresponding axes of reference passing through the temporomandibular joints and/or the eyes. The ability to measure not the antero-posterior angle of the real incisor occlusal plane in the anterior sagittal point, but only the two angles lateral thereto, will give rise—in the event of a latero-lateral inclination of the incisor plane—to different antero-posterior measurements depending on whether they are obtained on the right or left side of the head. The combined measurement may be useful to obtain fundamental information on the animal's present and future state of health inasmuch as an incorrect inclination of the incisor occlusal plane can severely restrict jaw movement, causing the animal recurrent discomfort.
Another disadvantage of the above-mentioned instrument lies in that simply holding the device up against the animal and keeping it in position while taking the measurement may not be easy, particularly if the animal moves.